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Chemical Formulas
Molecular compounds are composed of molecules and almost always contain only nonmetals.
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2. Diatomic Molecules
These seven elements occur naturally as molecules containing two atoms:
Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine
Bromine
Iodine
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3. Types of Formulas
Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound.
Molecular formulas give the exact number of atoms of each element in a compound.
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Types of Formulas
Structural formulas show the order in which atoms are bonded.
Perspective drawings also show the three-dimensional array of atoms in a compound.
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Ions
When atoms lose or gain electrons, they become ions.
Cations are positive and are formed by elements on the left side of the periodic chart.
Anions are negative and are formed by elements on the right side of the periodic chart.
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Ionic Bonds
Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.
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Writing Formulas
Because compounds are electrically neutral, one can determine the formula of a compound this way:
The charge on the cation becomes the subscript on the anion.
The charge on the anion becomes the subscript on the cation.
If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.
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